To answer my own questions...
After applying online, interviews were available the next day at the VAC (Visa Application Centre) in Toronto. The VAC really justs accepts the documents and passes them on to the UK High Commission.
My application took only 4 days to process with an approval (most likely because I have lots of job experience and a good deal of cash saved up), but I have heard of applications taking up to 10 weeks to process for Ancestry Visas. Another couple days for the passport to be returned to the VAC for pick up.
Obviously, this is my experience, and yours may vary.